I have set up the input and output points. I typed on the command history:

[A,B,C,D] = linmod('sistema_massa_molla')

This is what I got after it:

Warning: Using a default value of 0.4 for maximum step size. Thesimulation step size will be equal to or less than this value. You candisable this diagnostic by setting 'Automatic solver parameterselection' diagnostic to 'none' in the Diagnostics page of theconfiguration parameters dialog > In dlinmod at 202 In linmod at 60

A =

0 1.0000 0 -9.8100 -50.0000 0 0 0 0

B =

Empty matrix: 3-by-0

C =

Empty matrix: 0-by-3

D =

[]

Linmod result seems wrong to me: why I got 3x3 matrices ? Why are the B and C matrices null?